- 3349 - HUBBLE - giant planets and Europa? Hubble’s snapshots of the ‘outer planets” reveal both extreme and subtle changes rapidly taking place in these distant worlds. It gleans new insights into the fascinating, dynamic weather patterns and seasons on these gas giants and allows astronomers to investigate the very similar and very different causes of their changing atmospheres.
--------------------- 3349 - HUBBLE - giant planets and Europa?
- Hubble Space Telescope has visited the giant planets – Jupiter, Saturn, Uranus, and Neptune, extending as far as 30 times the distance between Earth and the Sun.
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- Unlike the rocky terrestrial planets like Earth and Mars that huddle close to the Sun’s warmth, these far-flung worlds are mostly composed of chilly gaseous soups of hydrogen, helium, ammonia, methane, and deep water around a packed, intensely hot, compact core.
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- Hubble’s longevity, and unique vantage point, has given astronomers a unique chance to check in on the outer planets on a yearly basis:
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---------------------------------------- Jupiter
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- This year’s 2021 Hubble images of Jupiter track the ever-changing landscape of its turbulent atmosphere, where several new storms are making their mark, and the pace of color changes near the planet’s equator is continuing to surprise researchers.
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- The planet’s equatorial zone has remained a deep orange hue for a much longer time, compared to previous darkening episodes. While the equator has changed from its traditional white or beige appearance for a few years now, scientists were surprised to find the deeper orange color to persist in Hubble’s recent imaging, instead expecting the zone to lose its reddish haze layer.
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- Just above the equator, researchers note the appearance of several new storms, nicknamed “barges” during the Voyager era. These elongated red cells can be defined as cyclonic vortexes, which vary in appearance. While some of the storms are sharply defined and clear, others are fuzzy and hazy. This difference in appearance is caused by the properties within the clouds of the vortexes.
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- When we look at Jupiter, in the barges or in the red band right below, we can see cloud structures that are clearly much deeper. We are seeing a lot of structure here and vertical depth variation.
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- The Great Red Spot has its winds speeding up, and is joined by a string of white, anti-cyclonic storms.
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-------------------------------------------- Saturn
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- Hubble’s new look at Saturn on September 12, 2021 shows rapid and extreme color changes of the bands in the planet’s northern hemisphere, where it is now early autumn. The bands have varied throughout Hubble observations in both 2019 and 2020.
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- Saturn’s iconic hexagonal storm, first discovered in 1981 by the Voyager 2 spacecraft, was difficult to distinguish in 2020, but it is again clearly evident in 2021. Hubble’s Saturn image catches the planet following the southern hemisphere’s winter, evident in the lingering blue-ish hue of the south pole.
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- If you were to look at this through a ground-based telescope, there’s some blurring with our atmosphere, and you’ll lose some of those color variations. Nothing from the ground will get visible-light images as sharp as Hubble’s.
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----------------------------------------------- Uranus
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- Hubble’s October 25, 2021 view of Uranus puts the planet’s bright northern polar hood in the spotlight. It’s springtime in the northern hemisphere and the increase in ultraviolet radiation absorbed from the Sun seems to be causing the polar region to brighten.
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- Researchers are studying how the brightening polar hood results from changes in the concentration of atmospheric methane gas and the characteristics of haze particles, as well as the atmospheric flow patterns.
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- Even as the atmospheric hood gets brighter, the sharp southernmost boundary remains fixed at the same latitude. This has been constant over the past several years observations, perhaps because a jet stream is setting up a barrier at that latitude of 43 degrees.
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----------------------------------------- Neptune
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- In observations taken on September 7, 2021 researchers found that Neptune’s dark spot, which recently was found to have reversed course from moving toward the equator, is still visible in this image, along with a darkened northern hemisphere. There is also a notable dark, elongated circle encompassing Neptune’s south pole.
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- Neptune's and Uranus’ blue color is a result of the absorption of red light by the planets’ methane-rich atmosphere, combined with the same Rayleigh-scattering process that makes the Earth's sky blue.
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- In 2021, there are few bright clouds on Neptune, and its distinct blue with a singular large dark spot is very reminiscent of what Voyager 2 saw in 1989.
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------------------------------------------- Europa
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- Jupiter's icy moon Europa have revealed the presence of persistent water vapor, but, mysteriously, only in one hemisphere. Europa harbors a vast ocean underneath its icy surface, which might offer conditions hospitable for life.
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- This result advances astronomers' understanding of the atmospheric structure of icy moons, and helps lay the groundwork for planned science missions to the Jovian system to explore whether an environment half-a-billion miles from the Sun could support life.
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- Slightly smaller than Earth's moon, Europa has a very smooth surface and the solid ice crust has the appearance of a cracked eggshell. The interior has a global ocean with more water than found on Earth. It could possibly harbor life as we know it.
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- Europa satellites have revealed the presence of persistent water vapor in its very tenuous atmosphere. Hubble observations, spanning 1999 to 2015, find that water vapor is constantly being replenished throughout one hemisphere of the moon.
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- This is a different finding from Hubble's 2013 observations that found localized water vapor from geysers venting from its subsurface ocean. This water vapor comes from a different process entirely. Sunlight causes the surface ice to sublimate, transitioning directly into gas.
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- Long, dark lines on the surface are fractures in the crust, some of which are more than 1,850 miles long. The Galileo mission ended on September 21, 2003, when the spacecraft was intentionally commanded to dive into Jupiter's atmosphere, where it was destroyed.
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- Previous observations of water vapor on Europa have been associated with plumes erupting through the ice. They are analogous to geysers on Earth, but extend more than 60 miles high. They produce transient blobs of water vapor in the moon's atmosphere, which is only one-billionth the surface pressure of Earth's atmosphere.
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- The new results show similar amounts of water vapor spread over a larger area of Europa in Hubble observations spanning from 1999 to 2015. This suggests a long-term presence of a water vapor atmosphere only in Europa's trailing hemisphere, that portion of the moon that is always opposite its direction of motion along its orbit. The cause of this asymmetry between the leading and trailing hemisphere is not fully understood.
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- The observation of water vapor on Ganymede, and on the trailing side of Europa, advances our understanding of the atmospheres of icy moons. The detection of a stable water abundance on Europa is a bit more surprising than on Ganymede because Europa's surface temperatures are lower than Ganymede's."
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- Europa reflects more sunlight than Ganymede, keeping the surface 60 degrees Fahrenheit cooler than Ganymede. The daytime high on Europa is a frigid -260°F. Yet, even at the lower temperature, the new observations suggest water ice is sublimating, transforming directly from solid to vapor without a liquid phase, off Europa's surface, just like on Ganymede.
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- Europa revealed the presence of persistent water vapor, but, mysteriously, only in one hemisphere. Europa harbors a vast ocean underneath its icy surface, which might offer conditions hospitable for life.
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- To make this discovery, datasets, selecting ultraviolet observations of Europa from 1999, 2012, 2014 and 2015 were studied while the moon was at various orbital positions. These observations were all taken with Hubble's “Space Telescope Imaging Spectrograph” (STIS).
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- The ultraviolet STIS observations were used to determine the abundance of oxygen in Europa's atmosphere, and by interpreting the strength of emission at different wavelengths was able to infer the presence of water vapor.
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- This detection paves the way for in-depth studies of Europa by future probes including NASA's “Europa Clipper” and the Jupiter Icy Moons Explorer mission from the European Space Agency (ESA). Understanding the formation and evolution of Jupiter and its moons also helps astronomers gain insights into Jupiter-like planets around other stars.
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November 20, 2021 HUBBLE - giant planets and Europa? 3349
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